1. Field of the Invention
The present invention relates to a pixel and an organic light emitting display using the same, and more particularly, to a pixel capable of improving display quality and an organic light emitting display using the same.
2. Description of the Related Art
Recently, various flat panel displays (FPD) capable of reducing weight and volume that are disadvantages of cathode ray tubes (CRT) have been developed. The FPDs include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the flat panel displays, the organic light emitting displays display images using organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes. The organic light emitting display has high response speed and is driven with low power consumption.
The organic light emitting display includes a plurality of pixels arranged at intersections of a plurality of data lines, scan lines, and power supply lines in a matrix. Each of the pixels commonly includes an organic light emitting diode (OLED), at least two transistors including a driving transistor, and at least one capacitor.
The organic light emitting display has advantage in that an amount of used power is small, however, has disadvantage in that an amount of current that flows to the OLEDs changes in accordance with deviation in the threshold voltages of the driving transistors included in the pixels so that non-uniformity in display is caused. That is, the characteristics of the driving transistors change in accordance with the manufacturing process variables of the driving transistors included in the pixels. Actually, it is not possible to manufacture the organic light emitting display so that all of the transistors of the organic light emitting display have the same characteristic in current processes so that the deviation in the threshold voltages of the driving transistors is generated.
In order to solve the problem, a method of adding compensating circuits each formed of a plurality of transistors and a capacitor to the pixels, respectively, is suggested. The compensating circuits included in each of the pixels charge voltages corresponding to the threshold voltages of the driving transistors in one horizontal period so that the deviation in the driving transistors is compensated for.
On the other hand, recently, in order to realize a three-dimensional image, a method of driving the organic light emitting display with a driving frequency of no less than 120 Hz is required. However, when the organic light emitting display is driven at high speed of no less than 120 Hz, a period of charging the threshold voltages of the driving transistors is reduced so that it is not possible to compensate for the threshold voltages of the driving transistors.
In addition, in a conventional art, a structure in which the voltages of driving power supplies (a first power supply ELVDD and a second power supply ELVSS) are controlled in order to drive the organic light emitting display at the speed of 120 Hz is suggested. However, when the driving power supplies are controlled, there are problems such as high power consumption, an increase in the probability of an erroneous operation due to a parasitic capacitor, and generation of large electromagnetic interference (EMI).